Firstly: Abstention from Nullifiers of Fasting
It is wajib for the fasting person to withhold from all nullifiers of his fast, like food, drink, and sexual intercourse. Consensus has been quoted over this by: Ibn Hazm, Ibn `Abd al-Barr, Ibn Taymiyyah.
Secondly: Covering the Full Period of Abstention
1. The beginning of the period of abstention
It is wajib for the fasting person to withhold from nullifiers from the entering of the second, real fajr.  There are two fajr, the true and false fajr. There are differences between them. They are: The false fajr is vertical in the sky, whereas the true fajr is horizontal, extending from north to south. The true fajr continues to grow in the intensity of its brightness, whereas the false fajr is followed by more darkness, which is why it is referred to as false. This is the position of the majority of scholars.
- Fajr entering while food is on the mouth
Whoever has food in his mouth then the time for fajr enters, then he must spit it out,  It is necessary to abstain as soon as the call is made if the one making it is trustworthy and does not make the call unless the time has entered. If, however, the caller makes his call before the entering of the time, then abstention is not obligatory, and it is permissible to eat and drink until fajr. Likewise if the fasting person is in open rural land, where he can visibly see the rise of fajr himself. Then, he does not have to abstain if the call is made if fajr is yet to enter. If he does not know the nature of the caller, whether he gives the call before or at fajr, then he must abstain if he hears it, since the origin is that it is given when the time enters. and if he swallows it, his fast is invalid. This is by agreement of the four schools of jurisprudence.
2. The ending of the time of withholding and related rulings
- When it ends
The time of withholding ends at sunset. Consensus has been quoted over this by: Ibn Hazm, Ibn `Abd al-Barr, and al-Nawawi.
- If the fasting person breaks his fast then he travels with an aeroplane and he sees the sun not set
If the sun has set and the fasting person has broken his fast, then he commenced a journey by aeroplane, where he saw the sun has not yet set when the aeroplane was high in the sky, he does not need to withhold and the fast which he concluded is valid. This is the verdict of `Abd al-Razzaq al-`Afifi, Ibn Baz, and Ibn `Uthaymin.
- What is relied upon for the time of breaking the fast for the person travelling by aeroplane
Whoever travels by aeroplane while fasting, then uses the time to check that sunset in his land of residency or a nearby land has taken place, but sees the sun still due to the height of the aeroplane, then he cannot break his fast until he sees the sun setting. This is the verdict of `Abd al-Razzaq al-`Afifi, Ibn Baz, and Ibn `Uthaymin.
- The time of breaking the fast for places where the day is long
It is wajib for the fasting person to withhold from the entering of fajr until sunset, regardless of how long the day is. This is as long as the day and night follow one another over twenty-four hours. If there is serious fear over one's health due to the long hours, then a concession of breaking the fast is available. Those days are then made up outside Ramadan, when they are able to or when the hours are more manageable. This is the verdict of Ibn Baz and Ibn `Uthaymin as well as others. It is also the decision of the International Islamic Fiqh Academy.
- Deciding the time for fajr and sunset in lands where they are abnormal
Whoever is in a land where the day and night do not follow one another in twenty-four hours, like a land who has constant daylight for days, weeks, or months, then they use the times of a neighbouring city where they do follow one another to estimate their time of withholding. This is the verdict of Ibn Baz and Ibn `Uthaymin as well as others. It is also the decision of the International Islamic Fiqh Academy.